The abuses peaked in 2008, when Mr. Tsvangirai won more votes than Mr. Mugabe in the election’s first round but withdrew from a runoff, saying he did not want anyone to be murdered for voting. About 200 of his supporters had already been killed.

Mr. Tsvangirai proved no match for Mr. Mugabe’s wily political maneuvering, which drew on his record as a leader in the struggle against white minority rule, his often violent intolerance of opposition, and his ability to marshal support from regional and broader African political forces.

Mr. Mugabe frequently inveighed against Britain, the former colonial power, and depicted his adversaries, including Mr. Tsvangirai, as puppets of the country’s former imperial overlords.

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Mr. Tsvangirai at a rally in Harare in October 2008. He won more votes than President Robert G. Mugabe in the first round of the presidential election, but withdrew from a runoff.Credit
Philimon Bulawayo/Reuters

When, in 2009, Mr. Tsvangirai became prime minister under a power-sharing agreement brokered by neighboring South Africa after the flawed vote of 2008, the pact and his new job diminished his ability to oppose the president.

Even as he accused Mr. Mugabe of flouting provisions of the so-called unity government, many critics said Mr. Tsvangirai had been outwitted and co-opted by the president. Indeed, once Mr. Mugabe’s sworn enemy, Mr. Tsvangirai seemed to settle into a more comfortable relationship with him, built on the privileges of office.

In 2012, after Mr. Tsvangirai celebrated his second marriage with a glitzy party attended by guests arriving in Bentleys, Mercedes and BMWs, some of his followers were aghast at the ostentatiousness of the display and questioned who had paid for it.

By the time elections were held the following year, Mr. Tsvangirai was greatly weakened. He accused Mr. Mugabe of rigging the election and challenged him in the courts. But Mr. Mugabe claimed victory with 61 percent of the vote, compared with 34 percent for Mr. Tsvangirai, and it seemed that Mr. Tsvangirai’s brush with high office was over. T hat was certainly Mr. Mugabe’s view.

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Mr. Tsvangirai arriving at Harare International Airport in January 2009 for power-sharing talks with Mr. Mugabe. He had been out of the country since the previous November.Credit
Philimon Bulawayo/Reuters

“We have thrown the enemy away like garbage,” Mr. Mugabe said. “We say to them: You are never going to rise again.”

For all that, Mr. Tsvangirai appeared in recent months to be attempting a comeback, even as he made frequent trips abroad for colon cancer treatment.

In 2017, he was part of a so-called united front with other opposition groups, including the Zimbabwe People First movement led by Joice Mujuru, a former vice president and onetime guerrilla fighter ousted by Mr. Mugabe in 2014.

After Mr. Mugabe was overthrown, there was fevered speculation that Mr. Mnangagwa would seek a more inclusive form of rule than the leader he had just ousted. Instead, Mr. Mnangagwa lauded Mr. Mugabe and announced a government of his own supporters, including the military.

Even as he fell ill with colon cancer, however, Mr. Tsvangirai failed to groom a successor, and he left behind a fractured party with no obvious leader to challenge Mr. Mnangagwa in the elections expected this year.

The eldest in a family of nine, Mr. Tsvangirai was born on March 10, 1952, in the Gutu district of Masvingo Province, in central Zimbabwe. The family was poor, and Mr. Tsvangirai abandoned formal schooling early to start work, first as a textile weaver and then as a plant foreman in a nickel mine.

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In June 2009, as prime minister of Zimbabwe, Mr. Tsvangirai met with President Barack Obama in the Oval Office.Credit
Doug Mills/The New York Times

He was married in 1978 to Susan Tsvangirai, with whom he had six children before her death in a car accident in 2009. (Mr. Tsvangirai was injured in the crash, with a truck near Harare, as was the car’s driver.) He married Elizabeth Macheka three years later.

His personal life at the time raised eyebrows. While he was planning to marry Ms. Macheka, another woman claimed to be his wife from a traditional ceremony in 2011. A court ruled in her favor.

A third woman also filed court papers claiming that she had been engaged to Mr. Tsvangirai. He eventually apologized publicly to his supporters.

“I had no intention to hurt anyone,” he said. “It was a genuine search.”

Like Mr. Mugabe and Mr. Mnangagwa, Mr. Tsvangirai was a member of the dominant Shona ethnic group. But while they chose armed resistance from exile in the so-called front-line states bordering what was then Rhodesia, Mr. Tsvangirai became a labor union leader, defending workers’ rights and rising through the ranks to be elected secretary general of the Zimbabwe Congress of Trade Unions in 1988.

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Mr. Tsvangirai with his wife, Elizabeth Mechaka, at a national policy conference in Harare in May 2013. In elections later that year, Mr. Mugabe claimed 61 percent of the vote to his 34 percent.Credit
Tsvangirayi Mukwazhi/Associated Press

His political roots in the labor movement set him apart from those like Mr. Mugabe and Mr. Mnangagwa, who drew their legitimacy from the seven-year war against white minority rule. Initially an ally, he became a thorn in the side of Mr. Mugabe and his ZANU-PF party.

But as the president’s intolerance became more evident, the gulf between the two men widened.

Famed for his vicious criticism of Mr. Mugabe’s government, Mr. Tsvangirai was twice detained during his time as a labor leader, the first time in 1989 after he voiced concern over rising state repression. Three years later, he was arrested for ignoring a ban on public protests ordered by Mr. Mugabe.

In 1999, he founded the Movement for Democratic Change as a challenger to Mr. Mugabe’s ZANU-PF Party. He soon discovered that opposition to Mr. Mugabe was a dangerous business.

In the late 1990s, he went on record in the local news media claiming that assailants had tried to throw him from his office window. In 2001, he narrowly escaped the hangman’s noose when he was tried on charges of plotting to kill Mr. Mugabe before the 2002 presidential election.

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Mr. Tsvangirai, left, at his home in Harare on Jan. 5, meeting with Emmerson Mnangagwa, Mr. Mugabe’s successor as president. Mr. Tsvangirai was being treated for cancer at the time.Credit
Jekesai Njikizana/Agence France-Presse — Getty Images

In 2003, Mr. Tsvangirai faced a treason charge for urging his party supporters to topple Mr. Mugabe’s government. The case was thrown out without going to trial.

Four years later, he was among many opposition supporters who were beaten as they tried to stage an antigovernment rally. Mr. Tsvangirai sustained head injuries that drew broad international media attention.

“Yes, they brutalized my flesh,” he said in a message from his hospital bed. “But they will never break my spirit. I will soldier on until Zimbabwe is free.”

Mr. Tsvangirai’s party split in two in 2005, when a faction led by Welshman Ncube, the party’s former secretary general, broke away.

The two sides disagreed on whether they should participate in planned Senate elections. Mr. Ncube thought the opposition should participate; Mr. Tsvangirai did not.

Then came the turmoil and bloodletting of 2008. Mr. Tsvangirai was initially optimistic about the future of the unity government, despite being denied an outright victory in the first round of voting, in which he had trounced Mr. Mugabe, his longtime rival.